Poor circulation is itself a medical condition, and also is often a complication or symptom of other medical conditions. In addition, poor circulation causes additional medical problems, such as ischemia (i.e., localized tissue anemia due to obstruction of the inflow of arterial blood) of various organs and tissue. Ischemia often causes significant pain, and ischemic pain is usually not responsive to narcotics.
In Raynaud's phenomenon, patients suffer painful ischemia, most commonly in the extremities, caused by vasospasm (i.e. acute constriction of arteries and arterioles) in the arterioles supplying the associated region. Also, some headaches likely result from cerebral vasospasm. In another example, patients with cardiac ischemia usually suffer from chest pain, among other symptoms. Severely restricted blood flow in the heart muscle is often caused by atherosclerosis (a disease of the arteries in which fatty material is deposited in the vessel wall, resulting in narrowing and eventual impairment of blood flow).
Arteriosclerosis (a chronic disease characterized by abnormal thickening and hardening of the arterial walls with resulting loss of elasticity) also causes a decrease in circulation. Renal artery stenosis (i.e., narrowing or blockage of the artery that supplies the kidney) is sometimes caused by arteriosclerosis or atherosclerosis. Renal artery stenosis, in turn, often causes hypertension. Another example, peripheral vascular disease, also known as arteriosclerosis of the extremities, occurs in about 6 out of 1,000 people.
These are just a few of the medical conditions that cause or are caused by poor circulation. Existing techniques for increasing blood flow include applying electrical stimulation to the skin, exercise, and vascular bypass grafting.
Other medical conditions cause or are caused by an unusually high rate of blood flow. For instance, some physicians believe that some migraine headaches are due at least in part to vasodilation (i.e., widening of the lumen of blood vessels) of certain cerebral or meningeal (i.e., one of the membranes enveloping the brain and spinal cord) arteries. Existing techniques for decreasing blood flow are primarily based on medication, e.g., sympathomimetic drugs that cause vasoconstriction.
All of the devices currently available for modulating circulatory perfusion have drawbacks. For instance, medications are typically not selective, as they may cause vasoconstriction or vasodilation throughout the body. Vascular bypass grafting is a highly invasive surgical procedure.
A method for treating peripheral vascular disease and organ ischemia by electrical stimulation with closed loop feedback control was published as U.S. Pat. No. 5,199,428 (the '428 patent) and U.S. Pat. No. 6,058,331 (the '331 patent). This method utilizes electrical stimulation of neural tissue. The extent of blood flow in a portion of the patient's body is sensed and neural tissue that project to the portion is electrically stimulated to increase the blood flow. The '331 patent indicates that blood flow is increased by reducing sympathetic neuronal activity in the affected portion of the patient's body. This technique is limited to electrical stimulation, and to applying the electrical stimulation to neural tissue. The '331 patent is further limited to using the electrical stimulation of neural tissue to reduce sympathetic activity.
What is needed is a selection of techniques for modulating circulatory perfusion, which allows physicians and patients to choose the best technique for each unique set of conditions. Also needed is the coupling of circulatory perfusion modulation with the administration of medications, and particularly, a chronic, fully implantable system for modulating circulatory perfusion while administering medication.